Nonlinear Indicial Response and Internal State-Space Representation and Its Applications on Delta Wing Aerodynamics

A modified nonlinear indicial response method, in conjunction with internal state-space representation (NIRISS) was proposed. It has been found that for a delta wing, its leading-edge vortex has a dominant effect on its aerodynamics and therefore the time-averaged vortex breakdown location is chosen as an internal variable to approximately describe the state of vortex flow over the delta wing. The response of this internal variable to arbitrary motion is estimated by a modified nonlinear indicial response functional. By means of a vortex filament method, this variable offers the additional information required at a given instant for calculating the surface pressure and airloads. Moreover, the method has been further applied to solve trajectories and the instantaneous pressure and air loads for a 65 wing in free-to-roll condition. The good comparisons between measured and predicted results, such as instantaneous pressures, airloads and free-to-roll motion history, show that within the framework of the proposed mathematical model, it is possible to apply this NIRISS method into the nonlinear flight regime.